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Discussion Starter · #1 ·
I have a customer who has two ductless heating/cooling units (for two lower floor rooms), floor heat (for 3 baths and one lower floor bedroom), 3 bathroom ceiling heaters rated at approx. 12 amps each, and a gas furnace. I calculated the ductless units, anticipated floor heat, and ceiling heaters and used my results in my final load calculation. However, I am not sure this is the correct way to do the calculation. You typically eliminate the smaller of AC vs Heat load. But, since the ductless provided both heat and cooling, I included it in the total heating load.
Also, I used the FLA or RLA on the nameplates shown below for my calculation. Is this the correct? I think so, but I would love to have some confirmation.


 

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Are you doing a load calc./demand factor for an existing panel? Each unit gets it's own circuit. Just go by name plate rating.
BTW the pic didn't post.
 

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Discussion Starter · #4 ·
Are you doing a load calc./demand factor for an existing panel? Each unit gets it's own circuit. Just go by name plate rating.
BTW the pic didn't post.
I replaced the existing 200A service. As I calculated the load, I have approx. 175A total connected load, using the standard method. I am not sure what's up with the pics. I tried to upload them twice.

As for the total connected load, that doesn't seem to leave much room for expansion... Maybe like a hot tub later on.
 

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Discussion Starter · #6 ·
Are you doing a load calc./demand factor for an existing panel? Each unit gets it's own circuit. Just go by name plate rating.
BTW the pic didn't post.
It's not really the branch circuit sizing that I am after, it's the total connected load calculation on the house that I am really after. I am doing a lot of work for this customer and she keeps adding stuff. I let her know she may be getting close to the limit on her 200A service. She says she will never get a hot tub, but I still like having lot's of room for expansion. If the total calculated load is now 175A, I would say she will not be able to add a normal 40A or 50A rated hot tub in the future without upgrading the service. (Sometimes people change their mind about things.)
 

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I replaced the existing 200A service. As I calculated the load, I have approx. 175A total connected load, using the standard method. I am not sure what's up with the pics. I tried to upload them twice.

As for the total connected load, that doesn't seem to leave much room for expansion... Maybe like a hot tub later on.
Is that total load including the ductless, and other heating units? Depending on the local climate, you can pretty much bet, they'll be running all the heaters, full bore, at the same time, so demand will be 100%, and continuous. Don't worry about the cooling load.
 

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Discussion Starter · #8 ·
Is that total load including the ductless, and other heating units? Depending on the local climate, you can pretty much bet, they'll be running all the heaters, full bore, at the same time, so demand will be 100%, and continuous. Don't worry about the cooling load.
Yes, it is the total calculated load, (175A.) I didn't add anything into my load calculation for continuous use...

Here's what I have:
2052 square ft living space
4 each small appliance circuits
1 each laundry circuits

After demand = 6730VA

Elec heating: 3 ceiling heat units 4320VA, floor heat approx. 1500VA, ductless units 8880VA

Total heating load =14700VA

Appliance load after demand = 3660VA
Dryer = 5000VA
Cooking (2 range units) = 11000VA

Total VA = 41090VA

41090VA / 240V = 171A

I have to leave the house now... I hope to be able to follow this. Thanks in advance for your patience.
 

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Paul .,

For the ductless unit genrally electric heating element is larger than cooling rating is.

However the sticky issue I know and I do ran into from time to time is heat pump ductless unit as long they dont have electric heating elements then you are fine with that but once you add electric heating element that useally go out of window due the KW rating of electric heaters.

So be aware of it. I dont know how cold it get in your area so it may affect how you rate the ductless unit with heat in there.

I dont know if they have demand caluations for multi units but if more than just couple units you may try a tip from apartment rating that may go in play for demand caluations.
 

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Discussion Starter · #10 · (Edited)
I'm not sure how these units work. From what little I know about them, or have read, it seems that they heat and cool by compressing or expanding the refrigerant used. I don't see anything on the nameplate about additional heating elements. I guess I'll have to ask the installer just to be sure.
 

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I'm not sure how these units work. From what little I know about them, or have read, it seems that they heat and cool by compressing or expanding the refrigerant used. I don't see anything on the nameplate about additional heating elements. I guess I'll have to ask the installer just to be sure.

These are heat pumps, they work similar to a normal AC unit, the biggest difference being they have the ability to reverse the flow of the refrigerant, which gives them the ability to both heat the air and cool the air. The only problem is they are pretty much useless as heaters when the outside temperature is about 35° F or lower. This is why the heat strips are sometimes needed, they don’t care how cold it is outside. A good indication that the unit is equipped with heat strips is a setting on the thermostat/remote/control face called “emergency heat”. If the installer added them himself, the added load won’t be included on the nameplate’s RLA, so good thing you can contact him haha
 

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The ductless splits I am familiar with usually do not have the electric aux/emer heat strip options. In colder climates most add a baseboard strip to supplement the heat pump.
 
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